Investments - Average Coupon Rate Percentage and the Average Days to Maturity of Debt (Detail) |
12 Months Ended | |
|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Commercial Paper [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 0.553% | |
| Average Days To Maturity | 154 days | |
| US Government Agencies [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 0.865% | |
| Average Days To Maturity | 599 days | |
| Municipal Bonds and Notes [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 0.528% | |
| Average Days To Maturity | 134 days | |
| Corporate Bonds and Notes [Member] | ||
| Schedule of Available-for-sale Securities [Line Items] | ||
| Average Coupon Rate | 1.757% | 1.828% |
| Average Days To Maturity | 331 days | 348 days |